Positioning systems, such as the Global Positioning System (GPS), provide signals to receivers, which allow the receivers to calculate a position on Earth using trilateration. GPS was originally developed for the U.S. Department of Defense for military and strategic uses. A mechanism called Selective Availability was used to introduce errors so that civilian navigation signals were significantly less accurate than military. In 2000, the Selective Availability mechanism was disabled and GPS signals available to the civilian population became as accurate as those available to military. This highly accurate positioning system, coupled with an influx of mobile devices, allowed for many location-based services to evolve.